Cell cycle regulated expression and phosphorylation of hpttg proto-oncogene product

Pituitary Tumor-Transforming Gene 1/Delta like Non-Canonical Notch Ligand 1 Signaling in Chronic Liver Diseases

The management of chronic liver diseases (CLDs) remains a challenge, and identifying effective treatments is a major unmet medical need. In the current review we focus on the pituitary tumor transforming gene (PTTG1)/delta like non-canonical notch ligand 1 (DLK1) axis as a potential therapeutic target to attenuate the progression of these pathological conditions. PTTG1 is a proto-oncogene involved in proliferation and metabolism. PTTG1 expression has been related to inflammation, angiogenesis, and fibrogenesis in cancer and experimental fibrosis. On the other hand, DLK1 has been identified as one of the most abundantly expressed PTTG1 targets in adipose tissue and has shown to contribute to hepatic fibrosis by promoting the activation of hepatic stellate cells. Here, we extensively analyze the increasing amount of information pointing to the PTTG1/DLK1 signaling pathway as an important player in the regulation of these disturbances. These data prompted us to hypothesize that activation of the PTTG1/DLK1 axis is a key factor upregulating the tissue remodeling mechanisms characteristic of CLDs. Therefore, disruption of this signaling pathway could be useful in the therapeutic management of CLDs.

Impact of RSUME Actions on Biomolecular Modifications in Physio-Pathological Processes

The small RWD domain-containing protein called RSUME or RWDD3 was cloned from pituitary tumor cells with increasing tumorigenic and angiogenic proficiency. RSUME expression is induced under hypoxia or heat shock and is upregulated, at several pathophysiological stages, in tissues like pituitary, kidney, heart, pancreas, or adrenal gland. To date, several factors with essential roles in endocrine-related cancer appear to be modulated by RWDD3. RSUME regulates, through its post-translational (PTM) modification, pituitary tumor transforming gene (PTTG) protein stability in pituitary tumors. Interestingly, in these tumors, another PTM, the regulation of EGFR levels by USP8, plays a pathogenic role. Furthermore, RSUME suppresses ubiquitin conjugation to hypoxia-inducible factor (HIF) by blocking VHL E3-ubiquitin ligase activity, contributing to the development of von Hippel-Lindau disease. RSUME enhances protein SUMOylation of specific targets involved in inflammation such as IkB and the glucocorticoid receptor. For many of its actions, RSUME associates with regulatory proteins of ubiquitin and SUMO cascades, such as the E2-SUMO conjugase Ubc9 or the E3 ubiquitin ligase VHL. New evidence about RSUME involvement in inflammatory and hypoxic conditions, such as cardiac tissue response to ischemia and neuropathic pain, and its role in several developmental processes, is discussed as well. Given the modulation of PTMs by RSUME in neuroendocrine tumors, we focus on its interactors and its mode of action. Insights into functional implications and molecular mechanisms of RSUME action on biomolecular modifications of key factors of pituitary adenomas and renal cell carcinoma provide renewed information about new targets to treat these pathologies.

Hypothalamic and ovarian transcriptome profiling reveals potential candidate genes in low and high egg production of white Muscovy ducks (Cairina moschata)

In China, the low egg production rate is a major challenge to Muscovy duck farmers. Hypothalamus and ovary play essential role in egg production of birds. However, there are little or no reports from these tissues to identify potential candidate genes responsible for egg production in White Muscovy ducks. A total of 1,537 laying ducks were raised; the egg production traits which include age at first egg (days), number of eggs at 300 d, and number of eggs at 59 wk were recorded. Moreover, 4 lowest (LP) and 4 highest producing (HP) were selected at 59 wk of age, respectively. To understand the mechanism of egg laying regulation, we sequenced the hypothalamus and ovary transcriptome profiles in LP and HP using RNA-Seq. The results showed that the number of eggs at 300 d and number of eggs at 59 wk in the HP were significantly more (P < 0.001) than the LP ducks. In total, 106.98G clean bases were generated from 16 libraries with an average of 6.68G clean bases for each library. Further analysis showed 569 and 2,259 differentially expressed genes (DEGs) were identified in the hypothalamus and ovary between LP and HP, respectively. The KEGG pathway enrichment analysis revealed 114 and 139 pathways in the hypothalamus and ovary, respectively which includes Calcium signaling pathway, ECM-receptor interaction, Focal adhesion, MAPK signaling pathway, Apoptosis and Apelin signaling pathways that are involved in egg production. Based on the GO terms and KEGG pathways results, 10 potential candidate genes (P2RX1, LPAR2, ADORA1, FN1, AKT3, ADCY5, ADCY8, MAP3K8, PXN, and PTTG1) were identified to be responsible for egg production. Further, protein-protein interaction was analyzed to show the relationship between these candidate genes. Therefore, this study provides useful information on transcriptome of hypothalamus and ovary of LP and HP Muscovy ducks.

Characterization of a novel separase-interacting protein and candidate new securin, Eip1p, in the fungal pathogen Candida albicans

Proper chromosome segregation is crucial for maintaining genomic stability and dependent on separase, a conserved and essential cohesin protease. Securins are key regulators of separases, but remain elusive in many organisms due to sequence divergence. Here, we demonstrate that the separase homologue Esp1p in the ascomycete Candida albicans, an important pathogen of humans, is essential for chromosome segregation. However, C. albicans lacks a sequence homologue of securins found in model ascomycetes. We sought a functional homologue through identifying Esp1p interacting factors. Affinity purification of Esp1p and mass spectrometry revealed Esp1p-Interacting Protein1 (Eip1p)/Orf19.955p, an uncharacterized protein specific to Candida species. Functional analyses demonstrated that Eip1p is important for chromosome segregation but not essential, and modulated in an APCCdc20-dependent manner, similar to securins. Eip1p is strongly enriched in response to methyl methanesulfate (MMS) or hydroxyurea (HU) treatment, and its depletion partially suppresses an MMS or HU-induced metaphase block. Further, Eip1p depletion reduces Mcd1p/Scc1p, a cohesin subunit and separase target. Thus, Eip1p may function as a securin. However, other defects in Eip1p-depleted cells suggest additional roles. Overall, the results introduce a candidate new securin, provide an approach for identifying these divergent proteins, reveal a putative anti-fungal therapeutic target, and highlight variations in mitotic regulation in eukaryotes.

Expression of Serum PTTG1 in Laryngeal Carcinoma and Its Correlation to Prognosis

Objectives.

The purpose of this study was to investigate serum pituitary tumor transforming gene (PTTG1) expression in laryngeal carcinoma and its relationship with the clinical pathological characteristics and prognosis.

Methods.

Expression of serum PTTG1 was measured by enzyme-linked immunosorbent assay in 110 patients with laryngeal carcinoma and 60 patients with vocal cord polyps. Expression of the serum PTTG1 levels relationship with the clinicopathological characteristics and prognosis were analyzed.

Results.

In laryngeal carcinoma patients’ serum, the PTTG1 median concentration was 141.43 pg/mL (interquartile range [IQR], 111.387 to 160.837 pg/mL), significantly higher than that of the vocal cord polyp group of 94.01 pg/mL (IQR, 81.26 to 108.59 pg/mL), and the difference was statistically significant (z=–6.715, P<0.001). PTTG1 expression with lymph node metastasis, clinical stage, and patients with laryngeal carcinoma was significantly correlated with the tumor differentiation degree (P<0.05). The total survival rate of the PTTG1 high expression group was significantly lower than the low expression group, and the difference of total survival time of the two groups was statistically significant (P<0.001).

Conclusion.

The PTTG1 expression level can be used as an index for evaluating prognosis of laryngeal cancer. High PTTG1 expression is one of the factors of poor prognosis of laryngeal carcinoma patients.

Identification of core genes and outcomes in hepatocellular carcinoma by bioinformatics analysis

Hepatocellular carcinoma (HCC) is the most common malignant liver disease in the world. However, the mechanistic relationships among various genes and signaling pathways are still largely unclear. In this study, we aimed to elucidate potential core candidate genes and pathways in HCC. The expression profiles GSE14520, GSE25097, GSE29721, and GSE62232, which cover 606 tumor and 550 nontumour samples, were downloaded from the Gene Expression Omnibus (GEO) database. Furthermore, HCC RNA-seq datasets were also downloaded from the Cancer Genome Atlas (TCGA) database. The differentially expressed genes (DEGs) were filtered using R software, and we performed gene ontology (GO) and Kyoto Encyclopedia of Gene and Genome (KEGG) pathway analysis using the online databases DAVID 6.8 and KOBAS 3.0. Furthermore, the protein-protein interaction (PPI) network complex of these DEGs was constructed by Cytoscape software, the molecular complex detection (MCODE) plug-in and the online database STRING. First, a total of 173 DEGs (41 upregulated and 132 downregulated) were identified that were aberrantly expressed in both the GEO and TCGA datasets. Second, GO analysis revealed that most of the DEGs were significantly enriched in extracellular exosomes, cytosol, extracellular region, and extracellular space. Signaling pathway analysis indicated that the DEGs had common pathways in metabolism-related pathways, cell cycle, and biological oxidations. Third, 146 nodes were identified from the DEG PPI network complex, and two important modules with a high degree were detected using the MCODE plug-in. In addition, 10 core genes were identified, TOP2A, NDC80, FOXM1, HMMR, KNTC1, PTTG1, FEN1, RFC4, SMC4, and PRC1. Finally, Kaplan-Meier analysis of overall survival and correlation analysis were applied to these genes. The abovementioned findings indicate that the identified core genes and pathways in this bioinformatics analysis could significantly enrich our understanding of the development and recurrence of HCC; furthermore, these candidate genes and pathways could be therapeutic targets for HCC treatment.

Pituitary tumor-transforming 1 expression in laryngeal cancer and its association with prognosis

The purpose of the present study was to investigate the association between the expression of pituitary tumor-transforming 1 (PTTG1) and the expression of matrix metalloproteinase (MMP)-2 and MMP-9 in laryngeal carcinoma tissues, and to elucidate the association between PTTG1 expression and the prognosis of patients with laryngeal cancer. Immunohistochemical staining was used to detect PTTG1 expression in laryngeal cancer and normal tumor-adjacent laryngeal tissues. Western blotting was used to determine the levels of PTTG1 and MMP-2 and -9 in laryngeal carcinoma tissues and to assess their correlation. In addition, the associations between PTTG1 expression and the clinical parameters of laryngeal cancer and patient survival were determined. The immunohistochemistry results revealed that the positive expression rates of PTTG1, MMP-2 and MMP-9 in the laryngeal cancer tissues were significantly higher than those in the carcinoma-adjacent normal laryngeal tissues (all P<0.05). In addition, expression levels of PTTG1, MMP-2 and MMP-9 were significantly associated with lymph node metastasis, histological grade and clinical stage (P<0.05). Furthermore, the levels of PTTG1 were positively correlated with the levels of MMP-2 and MMP-9 in laryngeal cancer tissues (P<0.05). In summary, the expression levels of PTTG1, MMP-2 and MMP-9 are closely associated with the biological behaviors of laryngeal cancer tissues, showing that they serve important roles in the occurrence and development of laryngeal cancer, and may be useful as biological indicators of laryngeal tissue invasion, metastasis and patient prognosis.

Protein stabilization by RSUME accounts for PTTG pituitary tumor abundance and oncogenicity

Increased levels of the proto-oncogene pituitary tumor-transforming gene 1 (PTTG) have been repeatedly reported in several human solid tumors, especially in endocrine-related tumors such as pituitary adenomas. Securin PTTG has a critical role in pituitary tumorigenesis. However, the cause of upregulation has not been found yet, despite analyses made at the gene, promoter and mRNA level that show that no mutations, epigenetic modifications or other mechanisms that deregulate its expression may explain its overexpression and action as an oncogene. We describe that high PTTG protein levels are induced by the RWD-containing sumoylation enhancer (RWDD3 or RSUME), a protein originally identified in the same pituitary tumor cell line in which PTTG was also cloned. We demonstrate that PTTG and RSUME have a positive expression correlation in human pituitary adenomas. RSUME increases PTTG protein in pituitary tumor cell lines, prolongs the half-life of PTTG protein and regulates the PTTG induction by estradiol. As a consequence, RSUME enhances PTTG transcription factor and securin activities. PTTG hyperactivity on the cell cycle resulted in recurrent and unequal divisions without cytokinesis, and the consequential appearance of aneuploidies and multinucleated cells in the tumor. RSUME knockdown diminishes securin PTTG and reduces its tumorigenic potential in a xenograft mouse model. Taken together, our findings show that PTTG high protein steady state levels account for PTTG tumor abundance and demonstrate a critical role of RSUME in this process in pituitary tumor cells.

Cloning of Porcine Pituitary Tumor Transforming Gene 1 and Its Expression in Porcine Oocytes and Embryos

The maternal-to-embryonic transition (MET) is a complex process that occurs during early mammalian embryogenesis and is characterized by activation of the zygotic genome, initiation of embryonic transcription, and replacement of maternal mRNA with embryonic mRNA. The objective of this study was to reveal the temporal expression and localization patterns of PTTG1 during early porcine embryonic development and to establish a relationship between PTTG1 and the MET. To achieve this goal, reverse transcription-polymerase chain reaction (RT-PCR) was performed to clone porcine PTTG1. Subsequently, germinal vesicle (GV)- and metaphase II (MII)-stage oocytes, zygotes, 2-, 4-, and 8-cell-stage embryos, morulas, and blastocysts were produced in vitro and their gene expression was analyzed. The results revealed that the coding sequence of porcine PTTG1 is 609-bp in length and that it encodes a 202-aa polypeptide. Using qRT-PCR, PTTG1 mRNA expression was observed to be maintained at high levels in GV- and MII-stage oocytes. The transcript levels in oocytes were also significantly higher than those in embryos from the zygote to blastocyst stages. Immunohistochemical analyses revealed that porcine PTTG1 was primarily localized to the cytoplasm and partially localized to the nucleus. Furthermore, the PTTG1 protein levels in MII-stage oocytes and zygotes were significantly higher than those in embryos from the 2-cell to blastocyst stage. After fertilization, the level of this protein began to decrease gradually until the blastocyst stage. The results of our study suggest that porcine PTTG1 is a new candidate maternal effect gene (MEG) that may participate in the processes of oocyte maturation and zygotic genome activation during porcine embryogenesis.

PTTG1 expression is associated with hyperproliferative disease and poor prognosis in multiple myeloma

Background

Multiple myeloma (MM) is an incurable haematological malignancy characterised by the clonal proliferation of malignant plasma cells within the bone marrow. We have previously identified pituitary tumour transforming gene 1 (Pttg1) as a gene that is significantly upregulated in the haematopoietic compartment of the myeloma-susceptible C57BL/KaLwRij mouse strain, when compared with the myeloma-resistant C57BL/6 mouse. Over-expression of PTTG1 has previously been associated with malignant progression and an enhanced proliferative capacity in solid tumours.

Methods

In this study, we investigated PTTG1 gene and protein expression in MM plasma cells from newly diagnosed MM patients. Gene expression profiling was used to identify gene signatures associated with high PTTG1 expression in MM patients. Additionally, we investigated the effect of short hairpin ribonucleic acid (shRNA)-mediated PTTG1 knockdown on the proliferation of the murine myeloma plasma cell line 5TGM1 in vitro and in vivo.

Results

PTTG1 was found to be over-expressed in 36–70 % of MM patients, relative to normal controls, with high PTTG1 expression being associated with poor patient outcomes (hazard ratio 2.49; 95 % CI 1.28 to 4.86; p = 0.0075; log-rank test). In addition, patients with high PTTG1 expression exhibited increased expression of cell proliferation-associated genes including CCNB1, CCNB2, CDK1, AURKA, BIRC5 and DEPDC1. Knockdown of Pttg1 in 5TGM1 cells decreased cellular proliferation, without affecting cell cycle distribution or viability, and decreased expression of Ccnb1, Birc5 and Depdc1 in vitro. Notably, Pttg1 knockdown significantly reduced MM tumour development in vivo, with an 83.2 % reduction in tumour burden at 4 weeks (p < 0.0001, two-way ANOVA).

Conclusions

This study supports a role for increased PTTG1 expression in augmenting tumour development in a subset of MM patients.

Electronic supplementary material

The online version of this article (doi:10.1186/s13045-015-0209-2) contains supplementary material, which is available to authorized users.

Prostate cancer cell response to paclitaxel is affected by abnormally expressed securin PTTG1

PTTG1 protein, the human securin, has a central role in sister chromatid separation during mitosis, and its altered expression has been reported in many tumor types. Paclitaxel is a widely used chemotherapeutic drug, whose mechanism of action is related to its ability to arrest cells in mitosis and the subsequent induction of the intrinsic apoptotic pathway. By using two prostate cancer cell lines with different responses to paclitaxel treatment, we have identified two situations in which PTTG1 influences cell fate differentially. In slippage-prone PC3 cells, both PTTG1 downregulation and overexpression induce an increase in mitotic cells that is associated with diminished apoptosis after paclitaxel treatment. In LNCaP cells, however, PTTG1 downregulation prevents mitotic entry and, subsequently, inhibits mitosis-associated, paclitaxel-induced apoptosis. In contrast, PTTG1 overexpression induces an increase in mitotic cells and apoptosis after paclitaxel treatment. We have also identified a role for Mcl-1 protein in preventing apoptosis during mitosis in PC3 cells, as simultaneous PTTG1 and Mcl-1 silencing enhances mitosis-associated apoptosis after paclitaxel treatment. The finding that a more efficient mitotic arrest alone in PC3 cells is not enough to increase apoptosis was also confirmed with the observation that a selected paclitaxel-resistant PC3 cell line showed an apoptosis-resistant phenotype associated with increased mitosis upon paclitaxel treatment. These findings could contribute to identify putative responsive and nonresponsive cells and help us to approach incomplete responses to paclitaxel in the clinical setting.

Down-regulation of the oncogene PTTG1 via the KLF6 tumor suppressor during induction of myeloid differentiation

The aberrant expression of proto-oncogenes is involved in processes that are responsible for cellular proliferation and the inhibition of myeloid differentiation in acute myeloid leukemia (AML). Pituitary Tumor-Transforming gene 1 (PTTG1), an oncogenic transcription factor, is abundantly expressed in various human cancers and hematopoietic malignancies. However, its expression in normal leukocytes and most normal tissues is very low or undetectable. The mechanism by which PTTG1 overexpression modifies myeloid cell development and promotes leukemogenesis remain unclear. To investigate the mechanistic links between PTTG1 overexpression and leukemia cell differentiation, we utilized phorbol 12-myristate 13-acetate (PMA), a well-known agent that triggers monocyte/macrophage differentiation, to analyze the expression patterns of PTTG1 in PMA-induced myeloid differentiation. We found that PTTG1 is down-regulated at the transcriptional level in PMA-treated HL-60 and THP1 cells. In addition, we identified a binding site for a tumor suppressor protein, Kruppel-like factor 6 (KLF6), in the PTTG1 promoter. We found that KLF6 could directly bind and repress PTTG1 expression. In HL-60 and THP1 cells, KLF6 mRNA and protein levels are up-regulated with a concordant reduction of PTTG1 expression upon treatment with PMA. Furthermore, KLF6 knockdown by shRNA abolished the suppression of PTTG1 and reduced the activation of the differentiation marker CD11b in PMA-primed cells. The protein kinase C (PKC) inhibitor and the MAPK/ERK kinase (MEK) inhibitor significantly blocked the potentiation of PMA-mediated KLF6 induction and the down-regulation of PTTG1, indicating that PTTG1 is suppressed via the activation of PKC/ERK/KLF6 pathway. Our findings suggest that drugs that increase the KLF6 inhibition of PTTG1 may have a therapeutic application in AML treatment strategies.

Securin enhances the anti-cancer effects of 6-methoxy-3-(3',4',5'-trimethoxy-benzoyl)-1H-indole (BPR0L075) in human colorectal cancer cells

BPR0L075 [6-methoxy-3-(3′,4′,5′-trimethoxy-benzoyl)-1H-indole] is a novel anti-microtubule drug with anti-tumor and anti-angiogenic activities in vitro and in vivo. Securin is required for genome stability, and is expressed abundantly in most cancer cells, promoting cell proliferation and tumorigenesis. In this study, we found that BPR0L075 efficiently induced cell death of HCT116 human colorectal cancer cells that have higher expression levels of securin. The cytotoxicity of BPR0L075 was attenuated in isogenic securin-null HCT116 cells. BPR0L075 induced DNA damage response, G₂/M arrest, and activation of the spindle assembly checkpoint in HCT116 cells. Interestingly, BPR0L075 induced phosphorylation of securin. BPR0L075 withdrawal resulted in degradation of securin, mitotic exit, and mitotic catastrophe, which were attenuated in securin-null cells. Inhibition of cdc2 decreased securin phosphorylation, G₂/M arrest and cell death induced by BPR0L075. Moreover, BPR0L075 caused cell death through a caspase-independent mechanism and activation of JNK and p38 MAPK pathways. These findings provided evidence for the first time that BPR0L075 treatment is beneficial for the treatment of human colorectal tumors with higher levels of securin. Thus, we suggest that the expression levels of securin may be a predictive factor for application in anti-cancer therapy with BPR0L075 in human cancer cells.

Pituitary tumor-transforming gene 1 enhances proliferation and suppresses early differentiation of keratinocytes

The epidermis is a self-renewing tissue, the homeostasis of which is dependent upon the tight balance between proliferation and differentiation based on appropriate regulation of the cell cycle. The cell cycle regulation is dependent on the interactions among a number of cell cycle regulatory molecules, including the pituitary tumor-transforming gene 1 (PTTG1), also known as securin, a regulator of sister chromatid separation and transition from metaphase to anaphase. This study was conducted to clarify the less-known functions of PTTG1 in the epidermis by the use of keratinocytes cultured under two-dimensional (2D) or three-dimensional (3D) conditions. Forced overexpression of PTTG1 caused upregulation of cyclin B1, cyclin-dependent kinase 1 (CDK1), and c-Myc, resulting in enhanced proliferation and suppression of early differentiation without apparent alterations in terminal differentiation, and the exogenous PTTG1 was downregulated in association with cell cycle exit. In contrast, depletion of PTTG1 caused their downregulation and constrained proliferation with retention of differentiation capacity. These findings suggested that PTTG1 could alter the proliferation status by modulating the expression levels of the other cell cycle regulatory proteins, and excess PTTG1 primarily affects early differentiation of keratinocytes under the stability regulation associated with cell cycle exit.

The pituitary tumor transforming gene in thyroid cancer

The pituitary tumor transforming gene (PTTG) is a multifunctional proto-oncogene that is over-expressed in various tumors including thyroid carcinomas, where it is a prognostic indicator of tumor recurrence. PTTG has potent transforming capabilities in vitro and in vivo, and many studies have investigated the potential mechanisms by which PTTG contributes to tumorigenesis. As the human securin, PTTG is involved in critical mechanisms of cell cycle regulation, whereby aberrant expression induces aneuploidy. PTTG may further contribute to tumorigenesis through its role in DNA damage response pathways and via complex interactions with hormones and growth factors. Furthermore, PTTG over-expression negatively impacts upon the efficacy of radioiodine therapy in thyroid cancer, through repression of expression and function of the sodium iodide symporter. Given its various roles at all disease stages, PTTG appears to be an important oncogene in thyroid cancer. This review discusses the current knowledge of PTTG with particular focus on its role in thyroid cancer.

Downregulation of protein tyrosine phosphatase PTPL1 alters cell cycle and upregulates invasion-related genes in prostate cancer cells

PTPL1, a non-receptor type protein tyrosine phosphatase, has been involved in the regulation of apoptosis and invasiveness of various tumour cell types, but its role in prostate cancer remained to be investigated. We report here that downregulation of PTPL1 by small interfering RNA in PC3 cells decreases cell proliferation and concomitantly reduces the expression of cell cycle-related proteins such as cyclins E and B1, PCNA, PTTG1 and phospho-histone H3. PTPL1 downregulation also increases the invasion ability of PC3 cells through Matrigel coated membranes. cDNA array of PTPL1-silenced PC3 cells versus control cells showed an upregulation of invasion-related genes such as uPA, uPAR, tPA, PAI-1, integrin α6 and osteopontin. This increased expression was also confirmed in PTPL1-silenced DU145 prostate cancer cells by quantitative real time PCR and western blot. These findings suggest that PTPL1 is an important mediator of central cellular processes such as proliferation and invasion.

Securin identifies a subgroup of patients with poor outcome in rectal cancer treated with long-course (chemo)radiotherapy

BACKGROUND

Securin is an oncogene with functions in cell proliferation, tumour initiation and progression. Its prognostic value in rectal cancer is somewhat unknown. Accordingly, we studied securin expression together with Ki-67 in rectal cancer in relation to preoperative (chemo)radiotherapy (RT) and disease outcome.

MATERIAL AND METHODS

Biopsies (n = 65 for securin; n = 57 for Ki-67) and operative specimens (n = 207) from 211 patients treated with short-course RT (n = 87), long-course RT (n = 54) or surgery only (n = 70) were studied with immunohistochemistry (IHC) for securin and Ki-67 expression. In the long-course RT group, 45 patients received chemotherapy (5-fluorouracil or capecitabine) concomitantly with RT. The results of IHC were related to clinicopathological variables, disease outcome and tumour regression grade (TRG) after long-course RT.

RESULTS

Both markers showed significant reduction after RT (p < 0.001). No differences in expression was seen in the long-course RT group between the patients with or without concomitant chemotherapy (p = 0.23 for securin; p = 0.31 for Ki-67). Low Ki-67 expression, but not that of securin, in operative specimens was significantly related to excellent TRG (p = 0.02 for Ki-67; p = 0.21 for securin). In univariate survival analysis, excellent TRG predicted longer disease-specific survival (DSS; p = 0.03). In multivariate Cox analysis, high securin expression after long-course (chemo)RT was an independent predictor of shorter DSS (p = 0.036) together with patient age (p = 0.043) and disease recurrence (local or distant; p = 0.009), whereas no similar appearance was seen in other treatment groups.

CONCLUSION

Securin expression in rectal cancer is significantly reduced after RT. High securin expression and poor TRG after long-course (chemo)RT are indicators of unfavourable disease outcome.

PTTG1/securin modulates microtubule nucleation and cell migration

PTTG1 is associated with the cis face of the Golgi apparatus and the centrosome, forming a complex with proteins involved in microtubule nucleation. PTTG1 depletion produces a delay in centrosomal and noncentrosomal microtubule nucleation and causes defects in both cell polarization and migration.

Pituitary tumor transforming gene 1 (PTTG1), also known as securin, has been implicated in many biological functions, including inhibition of sister chromatid separation, DNA repair, organ development, and regulation of the expression and secretion of angiogenic and metastatic factors. Although most of these functions of securin seem to depend on the localization of PTTG1 in the nucleus of the cell, a fraction of the protein has been also detected in the cytoplasm. Here we demonstrate that, in different cell types, a portion of cytoplasmic PTTG1 is associated with the cis face of the Golgi apparatus and that this localization depends on PTTG1 phosphorylation status. In this organelle, PTTG1 forms a complex with proteins involved in microtubule nucleation, including GM130, AKAP450, and γ-tubulin. RNA interference–mediated depletion of PTTG1 produces a delay in centrosomal and noncentrosomal microtubule nucleation. Cells lacking PTTG1 show severe defects in both cell polarization and migration in wound-healing assays. To our knowledge, this is the first study reporting the role of PTTG1 in microtubule nucleation and cell polarization, two processes directly involved in cell migration. We believe that these findings will contribute to understanding the mechanisms underlying PTTG1-mediated biological functions.

Glycogen synthase kinase-3beta (GSK3beta) negatively regulates PTTG1/human securin protein stability, and GSK3beta inactivation correlates with securin accumulation in breast tumors

PTTG1, also known as securin, is an inactivating partner of separase, the major effector for chromosome segregation during mitosis. At the metaphase-to-anaphase transition, securin is targeted for proteasomal destruction by the anaphase-promoting complex or cyclosome, allowing activation of separase. In addition, securin is overexpressed in metastatic or genomically instable tumors, suggesting a relevant role for securin in tumor progression. Stability of securin is regulated by phosphorylation; some phosphorylated forms are degraded out of mitosis, by the action of the SKP1-CUL1-F-box protein (SCF) complex. The kinases targeting securin for proteolysis have not been identified, and mechanistic insight into the cause of securin accumulation in human cancers is lacking. Here, we demonstrate that glycogen synthase kinase-3β (GSK3β) phosphorylates securin to promote its proteolysis via SCF(βTrCP) E3 ubiquitin ligase. Importantly, a strong correlation between securin accumulation and GSK3β inactivation was observed in breast cancer tissues, indicating that GSK3β inactivation may account for securin accumulation in breast cancers.

Identification of a common gene expression signature associated with immature clonal mesenchymal cell populations derived from bone marrow and dental tissues

Mesenchymal stem/stromal cell-like populations derived from adult bone marrow (BMSC), dental pulp (DPSC), and periodontal ligament (PDLSC) have the ability to differentiate into cells of mesenchymal and non-mesenchymal tissues in vitro and in vivo. However, culture-expanded MSC-like populations are a heterogeneous mix of stem/committed progenitor cells that exhibit altered growth and developmental potentials. In the present study we isolated and characterized clonal populations of BMSCs, DPSCs, and PDLSCs to identify potential biomarkers associated with long-lived multipotential stem cells. Microarray analysis was used to compare the global gene expression profiles of high growth/multipotential clones with low growth potential cell clones derived from 3 stromal tissues. Cross-comparison analyses of genes expressed by high growth/multipotential clones derived from bone marrow, dental pulp, and periodontal ligament identified 24 genes that are differentially up-regulated in all tissues. Notably, the transcription factors, E2F2, PTTG1, TWIST-1, and transcriptional cofactor, LDB2, each with critical roles in cell growth and survival, were highly expressed in all stem cell populations examined. These findings provide a model system for identifying a common molecular fingerprint associated with immature mesenchymal stem-like cells from different organs and implicate a potential role for these genes in MSC growth and development.

Pituitary tumor-transforming gene and its binding factor in endocrine cancer

The pituitary tumor-transforming gene (PTTG1) encodes a multifunctional protein (PTTG) that is overexpressed in numerous tumours, including pituitary, thyroid, breast and ovarian carcinomas. PTTG induces cellular transformation in vitro and tumourigenesis in vivo, and several mechanisms by which PTTG contributes to tumourigenesis have been investigated. Also known as the human securin, PTTG is involved in cell cycle regulation, controlling the segregation of sister chromatids during mitosis. This review outlines current information regarding PTTG structure, expression, regulation and function in the pathogenesis of neoplasia. Recent progress concerning the use of PTTG as a prognostic marker or therapeutic target will be considered. In addition, the PTTG binding factor (PBF), identified through its interaction with PTTG, has also been established as a proto-oncogene that is upregulated in several cancers. Current knowledge regarding PBF is outlined and its role both independently and alongside PTTG in endocrine and related cancers is discussed.

Regulation of post-translational protein arginine methylation during HeLa cell cycle

BACKGROUND

Post-translational arginine methylation which modifies protein-arginyl residues by protein arginine methyltransferase (PRMT) was investigated during synchronized HeLa cell cycle.

METHODS

The lysates of cells synchronized at each stage were subjected to one and/or two dimensional electrophoresis followed by Western immunoblot using against anti-asymmetric-dimethyl-arginine (ASYM24), anti-symmetric-dimethyl-arginine (SYM10), and subclasses of PRMTs, including PRMT1, PRMT3, PRMT4 (CARM1), PRMT5, PRMT6, and PRMT7 antibodies.

RESULTS

Proteins with approximate molecular masses of 80 kDa, 68 kDa, and 64 kDa, containing asymmetric-dimethyl-arginine (aDMA) were increased at G0/G1 to G1, which lasted until S phase. In addition, 25 kDa protein of symmetric-dimethyl-arginine (sDMA) was also markedly up-regulated from G0/G1 to G1. The levels of PRMT3, PRMT6 and PRMT7 were concurrently increased during the cell cycle. Two-dimensional gel electrophoresis followed by MALDI-TOF-MS was identified as aDMA-80 kDa and aDMA-68 kDa proteins as heterogeneous nuclear ribonucleoprotein R (hnRNPR), aDMA-64 kDa proteins as cleavage stimulation factor 64 kDa subunit (CstF-64), and sDMA-25 kDa protein as triosephosphate isomerase (TPI). The levels of increased aDMA of hnRNPR were reduced, when HeLa cells were transfected with siRNA for PRMT1, and the aDMA of CstF-64 with siRNA for PRMT3, while depletion of PRMT5 down-regulated sDMA of TPI.

CONCLUSION

Protein arginine dimethylations of hnRNPR, CstF-64, and TPI were regulated during HeLa cell cycle by respective PRMTs.

GENERAL SIGNIFICANCE

These results suggest that regulation of arginine dimethylation of hnRNPR, CstF-64, and TPI at G0/G1 to G1 are most likely to modulate the cellular growth and proliferation in HeLa cell cycle.

Expression of pituitary tumor-transforming gene 1 (PTTG1)/securin in hepatitis B virus (HBV)-associated liver diseases: evidence for an HBV X protein-mediated inhibition of PTTG1 ubiquitination and degradation

Chronic infection with hepatitis B virus (HBV) is strongly associated with hepatocellular carcinoma (HCC), and the viral HBx protein plays a crucial role in the pathogenesis of liver tumors. Because the protooncogene pituitary tumor-transforming gene 1 (PTTG1) is overexpressed in HCC, we investigated the regulation of this protein by HBx. We analyzed PTTG1 expression levels in liver biopsies from patients chronically infected with HBV, presenting different disease stages, and from HBx transgenic mice. PTTG1 was undetectable in biopsies from chronic hepatitis B patients or from normal mouse livers. In contrast, hyperplastic livers from transgenic mice and biopsies from patients with cirrhosis, presented PTTG1 expression which was found mainly in HBx-expressing hepatocytes. PTTG1 staining was further increased in HCC specimens. Experiments in vitro revealed that HBx induced a marked accumulation of PTTG1 protein without affecting its messenger RNA levels. HBx expression promoted the inhibition of PTTG1 ubiquitination, which in turn impaired its degradation by the proteasome. Glutathione S-transferase pull-down and co-immunoprecipitation experiments demonstrated that the interaction between PTTG1 and the Skp1-Cul1-F-box ubiquitin ligase complex (SCF) was partially disrupted, possibly through a mechanism involving protein-protein interactions of HBx with PTTG1 and/or SCF. Furthermore, confocal analysis revealed that HBx colocalized with PTTG1 and Cul1. We propose that HBx promotes an abnormal accumulation of PTTG1, which may provide new insights into the molecular mechanisms of HBV-related pathogenesis of progressive liver disease leading to HCC development.

Effect of PTTG on endogenous gene expression in HEK 293 cells

Background

Pituitary tumor transforming gene (PTTG), also known as securin, is highly expressed in various tumors including pituitary, thyroid, colon, ovary, testis, lung, and breast. An overexpression of PTTG enhances cell proliferation, induces cellular transformation in vitro, and promotes tumor development in nude mice. PTTG also inhibits separation of sister chromatids leading to aneuploidy and genetic instability. A great amount of work has been undertaken to understand the biology of PTTG and its expression in various tumors. However, mechanisms by which PTTG mediates its tumorigenic function are not fully understood. To utilize this gene for cancer therapy, identification of the downstream signaling genes regulated by PTTG in mediation of its tumorigenic function is necessary. For this purpose, we expressed PTTG in human embryonic kidney (HEK293) cells that do not express PTTG and analyzed the downstream genes using microarray analysis.

Results

A total of 22,277 genes printed on an Affymetrix HG-U133A 2.0 GeneChip™ array were screened with labeled cRNA prepared from HEK293 cells infected with adenovirus vector expressing PTTG cDNA (AdPTTG cDNA) and compared with labeled cRNA prepared from HEK293 cells infected with control adenovirus (control Ad) or adenovirus vector expressing GFP (AdGFP). Out of 22,277 genes, 71 genes were down-regulated and 35 genes were up-regulated with an FDR corrected p-value of ≤ 0.05 and a fold change of ≥2. Most of the altered genes identified are involved in the cell cycle and cell apoptosis; a few are involved in mRNA processing and nitrogen metabolism. Most of the up-regulated genes belong to the histone protein family.

Conclusion

PTTG is a well-studied oncogene for its role in tumorigenesis. In addition to its importance in regulation of the cell cycle, this gene has also been recently shown to play a role in the induction of cell apoptosis. The microarray analysis in the present study demonstrated that PTTG may induce apoptosis by down-regulation of oncogenes such as v-Jun and v-maf and up-regulation of the histone family of genes.

The pathogenesis of pituitary tumors

Recently there has been significant progress in our understanding of pituitary development, physiology, and pathology. New information has helped to clarify the classification of pituitary tumors. Epidemiologic analyses have identified a much higher incidence of pituitary tumors than previously thought. We review the pathogenetic factors that have been implicated in pituitary tumorigenesis and the application of novel targeted therapies that underscore the increasingly important role of the pathologist in determining accurate diagnoses and facilitating appropriate treatment of patients with these disorders.

PTTG: an important target gene for ovarian cancer therapy

Pituitary tumor transforming gene (PTTG), also known as securin is an important gene involved in many biological functions including inhibition of sister chromatid separation, DNA repair, organ development, and expression and secretion of angiogenic and metastatic factors. Proliferating cancer cells and most tumors express high levels of PTTG. Overexpression of PTTG in vitro induces cellular transformation and development of tumors in nude mice. The PTTG expression levels have been correlated with tumor progression, invasion, and metastasis. Recent studies show that down regulation of PTTG in tumor cell lines and tumors in vivo results in suppression of tumor growth, suggesting its important role in tumorigenesis. In this review, we focus on PTTG structure, sub-cellular distribution, cellular functions, and role in tumor progression with suggestions on possible exploration of this gene for cancer therapy.

Dicoumarol down-regulates human PTTG1/Securin mRNA expression through inhibition of Hsp90

Securin, the natural inhibitor of sister chromatid untimely separation, is a protooncogene overexpressed in tumors. Its protein levels correlate with malignancy and metastatic proneness. Dicoumarol, a long-established oral anticoagulant, is a new Hsp90 inhibitor that represses PTTG1/Securin gene expression and provokes apoptosis through a complex trait involving both intrinsic and extrinsic pathways. Dicoumarol activity as an Hsp90 inhibitor is confirmed by smaller levels of Hsp90 clients in treated cells and inhibition of in vivo heat shock luciferase activity recovery assays. Likewise, established Hsp90 inhibitors (17-allylamino-geldanamycin and novobiocin) repress PTTG1/Securin gene expression. Also, overexpression of human Hsp90 in yeast makes them hypersensitive to dicoumarol. Both apoptosis and PTTG1/Securin gene repression exerted by dicoumarol in cancer cells are independent of three of the most important signaling pathways affected by Hsp90 inhibition: nuclear factor-kappaB, p53, or Akt/protein kinase B signaling pathways. However, effects on PTTG1/Securin could be partially ascribed to inhibition of the Ras/Raf/extracellular signal-regulated kinase pathway. Overall, we show that expression of PTTG1/Securin gene is Hsp90 dependent and that dicoumarol is a bona fide Hsp90 inhibitor. These findings are important to understand the mode of action of Hsp90 inhibitors, mechanisms of action of dicoumarol, and Securin overexpression in tumors.

The important anti-apoptotic role and its regulation mechanism of PTTG1 in UV-induced apoptosis

Pituitary tumor transforming gene (PTTG1) is widely detected in many tumors. Increasing evidence reveals that PTTG1 is associated with cell proliferation, cellular transformation and apoptosis. However, the functions of PTTG1, especially its role in DNA damage-induced apoptosis, remain largely unclear. In this report, we used UV irradiation to induce apoptosis in HeLa cells to examine the role of PTTG1 in UV-induced apoptosis by RNAi-mediated knockdown and overexpression of PTTG1. RNAi-mediated knockdown of PTTG1 expression increased and overexpression of PTTG1 decreased the UV-induced apoptosis. Furthermore, UV irradiation decreased PTTG1 mRNA and protein expression. These effects were found to be mediated by JNK pathway. Therefore, PTTG1 had an important anti-apoptotic role in UV-induced apoptosis and this role was mediated by JNK pathway. These results may provide important information for understanding the exact role and the regulation mechanism of PTTG1 in UV-induced apoptosis.

Pituitary tumor-transforming gene: physiology and implications for tumorigenesis

Pituitary tumor-transforming gene-1 (PTTG1) is overexpressed in a variety of endocrine-related tumors, especially pituitary, thyroid, breast, ovarian, and uterine tumors, as well as nonendocrine-related cancers involving the central nervous, pulmonary, and gastrointestinal systems. Forced PTTG1 expression induces cell transformation in vitro and tumor formation in nude mice. In some tumors, high PTTG1 levels correlate with invasiveness, and PTTG1 has been identified as a key signature gene associated with tumor metastasis. Increasing evidence supports a multifunctional role of PTTG1 in cell physiology and tumorigenesis. Physiological PTTG1 properties include securin activity, DNA damage/repair regulation and involvement in organ development and metabolism. Tumorigenic mechanisms for PTTG1 action involve cell transformation and aneuploidy, apoptosis, and tumorigenic microenvironment feedback. This paper reviews recent advances in our understanding of PTTG1 structure and regulation and addresses known mechanisms of PTTG1 action. Recent knowledge gained from PTTG1-null mouse models and transgenic animals and their potential application to subcellular therapeutic targeting PTTG1 are discussed.

p53 stabilization can be uncoupled from its role in transcriptional activation by loss of PTTG1/securin

HCT116 cells devoid of PTTG1/securin (sec(-/-) HCT116) show a stabilized yet transcriptionally latent form of p53 protein in the absence of DNA damage. Ser15, Ser20 phosphorylation and other post-transcriptional modifications of p53 resolved by 2D gel electrophoresis are comparable to that observed in sec(+/+) HCT116 cells. The difference in degradation was also shown to be independent of the ubiquitin system but reliant on calpains. However, the p53-mediated checkpoint response is active only after genotoxic stress in sec(-/-) HCT116 cells. These findings point to the calpain pathway as a key player to maintain steady state levels of p53 in resting cells without affecting its activity.

Novel functions of thyroid hormone receptor mutants: beyond nucleus-initiated transcription

Study of molecular actions of thyroid hormone receptor beta (TRbeta) mutants in vivo has been facilitated by creation of a mouse model (TRbetaPV mouse) that harbors a knockin mutant of TRbeta (denoted PV). PV, which was identified in a patient with resistance to thyroid hormone, has lost T3 binding activity and transcription capacity. The striking phenotype of thyroid cancer exhibited by TRbeta(PV/PV) mice has allowed the elucidation of novel oncogenic activity of a TRbeta mutant (PV) [PAS1] beyond nucleus-initiated transcription. PV was found to physically interact with the regulatory p85alpha subunit of phosphatidylinositol 3-kinase (PI3K) in both the nuclear and cytoplasmic compartments. This protein-protein interaction activates the PI3K signaling by increasing phosphorylation of AKT, mammalian target of rapamycin (mTOR), and p70(S6K). PV, via interaction with p85alpha, also activates the PI3K-integrin-linked kinase-matrix metalloproteinase-2 signaling pathway in the extra-nuclear compartment. The PV-mediated PI3K activation results in increased cell proliferation, motility, migration, and metastasis. In addition to affecting these membrane-initiated signaling events, PV affects the stability of the pituitary tumor-transforming gene (PTTG) product. PTTG (also known as securin), a critical mitotic checkpoint protein, is physically associated with TRbeta or PV in vivo. Concomitant with T3-induced degradation of TRbeta, PTTG is degraded by the proteasome machinery, but no such degradation occurs when PTTG is associated with PV. The degradation of PTTG/TRbeta is activated by the direct interaction of the T3-bound TRbeta with the steroid receptor coactivator-3 (SRC-3) that recruits a proteasome activator (PA28gamma). PV that does not bind T3 cannot interact directly with SRC-3/PA28gamma to activate proteasome degradation, and the absence of degradation results in an aberrant accumulation of PTTG. The PV-induced failure of timely degradation of PTTG results in mitotic abnormalities. PV, via novel protein-protein interaction and transcription regulation, acts to antagonize the functions of wild-type TRs and contributes to the oncogenic functions of this mutation.

PTTG is a secretory protein in human pituitary adenomas and in mouse pituitary tumor cell lines

The pituitary tumor-transforming gene (PTTG) is a homolog of yeast Securin, which arrests the activation of Separin to induce sister chromatid separation in the transition from metaphase to anaphase. Pituitary tumor-transforming gene is also known to induce angiogenesis during pituitary tumorigenesis. It has not been clarified whether PTTG functions as a cytoplasmic or a nuclear protein. Our immunohistochemical study indicated that PTTG is localized in the cytoplasm of pituitary tumor cells. In the present study, confocal laser scanning microscopy (CLSM) analysis of human pituitary adenomas and immunoelectron microscopy of the mouse pituitary cell line, AtT-20, demonstrated the localization of PTTG in the Golgi apparatus and vesicles. Secreted PTTG was detected by immunoblotting from culture medium of mouse pituitary tumor cell lines. Our results suggested that PTTG is a secretory protein produced by pituitary tumor cells. In addition, PTTG may exert autocrine and/or paracrine functions as a newly proposed important pathway for the action of PTTG.

Regulation of angiogenesis and invasion by human Pituitary tumor transforming gene (PTTG) through increased expression and secretion of matrix metalloproteinase-2 (MMP-2)

Background

Pituitary tumor transforming gene (PTTG) is a novel oncogene that is expressed at higher level in most of the tumors analyzed to date compared to normal tissues. Existence of a relationship between PTTG levels and tumor angiogenesis and metastasis has been reported. However, the mechanisms by which PTTG achieve these functions remain unknown. In the present study, we investigated the effect of overexpression of PTTG on secretion and expression of metastasis-related metalloproteinase-2 (MMP-2) in HEK293 cells, cell migration, invasion and tubule formation.

Results

Transient or stable transfection of HEK293 cells with PTTG cDNA showed a significant increase in secretion and expression of MMP-2 measured by zymography, reverse transcriptase (RT/PCR), ELISA, and MMP-2 gene promoter activity. Furthermore, in our studies, we showed that tumor developed in nude mice on injection of HEK293 cells that constitutively express PTTG expressed high levels of both MMP-2 mRNA and protein, and MMP-2 activity. Conditioned medium collected from the HEK293 cells overexpressing PTTG showed a significant increase in cell migration, invasion and tubule formation of human umbilical vein endothelial cells (HUVEC). Pretreatment of conditioned medium with MMP-2-specific antibody significantly decreased these effects, suggesting that PTTG may contribute to tumor angiogenesis and metastasis via activation of proteolysis and increase in invasion through modulation of MMP-2 activity and expression.

Conclusion

Our results provide novel information that PTTG contributes to cell migration, invasion and angiogenesis by induction of MMP-2 secretion and expression. Furthermore, we showed that tumors developed in nude mice on injection of HEK293 cells that constitutively express PTTG induce expression of MMP-2 and significantly increase its functional activity, suggesting a relationship between PTTG levels and MMP-2 which may play a critical role in regulation of tumor growth, angiogenesis and metastasis. Blocking of function of PTTG or down regulation of its expression in tumors may result in suppression of tumor growth and metastasis, through the down regulation of MMP-2 expression and activity. To our knowledge, this study is the first study demonstrating the modulation of MMP-2 expression and biological activity by PTTG.

Aberrant accumulation of PTTG1 induced by a mutated thyroid hormone beta receptor inhibits mitotic progression

Overexpression of pituitary tumor-transforming 1 (PTTG1) is associated with thyroid cancer. We found elevated PTTG1 levels in the thyroid tumors of a mouse model of follicular thyroid carcinoma (TRbeta(PV/PV) mice). Here we examined the molecular mechanisms underlying elevated PTTG1 levels and the contribution of increased PTTG1 to thyroid carcinogenesis. We showed that PTTG1 was physically associated with thyroid hormone beta receptor (TRbeta) as well as its mutant, designated PV. Concomitant with thyroid hormone-induced (T3-induced) degradation of TRbeta, PTTG1 proteins were degraded by the proteasomal machinery, but no such degradation occurred when PTTG1 was associated with PV. The degradation of PTTG1/TRbeta was activated by the direct interaction of the liganded TRbeta with steroid receptor coactivator 3 (SRC-3), which recruits proteasome activator PA28gamma. PV, which does not bind T3, could not interact directly with SRC-3/PA28gamma to activate proteasome degradation, resulting in elevated PTTG1 levels. The accumulated PTTG1 impeded mitotic progression in cells expressing PV. Our results unveil what we believe to be a novel mechanism by which PTTG1, an oncogene, is regulated by the liganded TRbeta. The loss of this regulatory function in PV led to an aberrant accumulation of PTTG1 disrupting mitotic progression that could contribute to thyroid carcinogenesis.

Pituitary tumor-transforming gene expression is a prognostic marker for tumor recurrence in squamous cell carcinoma of the head and neck

Background

The proto-oncogene pituitary tumor-transforming gene (PTTG) has been shown to be abundantly overexpressed in a large variety of neoplasms likely promoting neo-vascularization and tumor invasiveness. In this study, we investigated a potential role for PTTG mRNA expression as a marker to evaluate the future clinical outcome of patients diagnosed with primary cancer of the head and neck.

Methods

Tumor samples derived from primary tumors of 89 patients suffering from a squamous cell carcinoma were analyzed for PTTG mRNA-expression and compared to corresponding unaffected tissue. Expression levels were correlated to standard clinico-pathological parameters based on a five year observation period.

Results

In almost all 89 tumor samples PTTG was found to be overexpressed (median fold increase: 2.1) when compared to the unaffected tissue specimens derived from the same patient. The nodal stage correlated with PTTG transcript levels with significant differences between pN0 (median expression: 1.32) and pN+ (median expression: 2.12; P = 0.016). In patients who developed a tumor recurrence we detected a significantly higher PTTG expression in primary tumors (median expression: 2.63) when compared to patients who did not develop a tumor recurrence (median expression: 1.29; P = 0.009). Since the median expression of PTTG in patients with tumor stage T1/2N0M0 that received surgery alone without tumor recurrence was 0.94 versus 3.82 in patients suffering from a tumor recurrence (P = 0.006), PTTG expression might provide a feasible mean of predicting tumor recurrence.

Conclusion

Elevated PTTG transcript levels might be used as a prognostic biomarker for future clinical outcome (i.e. recurrence) in primary squamous cell carcinomas of the head and neck, especially in early stages of tumor development.

Securin (hPTTG1) expression is regulated by beta-catenin/TCF in human colorectal carcinoma

Overexpression of the transcriptional activator β-catenin, mostly owing to loss-of-function mutations of the adenomatous polyposis coli (APC) tumour suppressor gene, is crucial for the initiation and progression of human colorectal carcinogenesis. Securin is a regulator of chromosome separation and its overexpression has been shown to be involved in different tumour-promoting processes, like transformation, hyperproliferation and angiogenesis, and correlates with tumour cell invasion. However, the molecular mechanism leading to securin overexpression in human colorectal cancer is unknown. Here we show a correlated high expression of β-catenin and securin (hPTTG1) in colorectal adenomas and carcinomas and further demonstrate that securin is a target of β-catenin transcriptional activation. This implies that deregulation of the β-catenin/T-cell factor-signalling pathway leads to overexpression of securin in human colorectal cancer, which subsequently may contribute to tumour progression.

Protein phosphatase 2A stabilizes human securin, whose phosphorylated forms are degraded via the SCF ubiquitin ligase

Sister chromatid segregation is triggered at the metaphase-to-anaphase transition by the activation of the protease separase. For most of the cell cycle, separase activity is kept in check by its association with the inhibitory chaperone securin. Activation of separase occurs at anaphase onset, when securin is targeted for destruction by the anaphase-promoting complex or cyclosome E3 ubiquitin protein ligase. This results in the release of the cohesins from chromosomes, which in turn allows the segregation of sister chromatids to opposite spindle poles. Here we show that human securin (hSecurin) forms a complex with enzymatically active protein phosphatase 2A (PP2A) and that it is a substrate of the phosphatase, both in vitro and in vivo. Treatment of cells with okadaic acid, a potent inhibitor of PP2A, results in various hyperphosphorylated forms of hSecurin which are extremely unstable, due to the action of the Skp1/Cul1/F-box protein complex ubiquitin ligase. We propose that PP2A regulates hSecurin levels by counteracting its phosphorylation, which promotes its degradation. Misregulation of this process may lead to the formation of tumors, in which overproduction of hSecurin is often observed.

PTTG overexpression is correlated with angiogenesis in human pituitary adenomas

Human pituitary tumor transforming gene (hPTTG1) was recently identified as a protooncogene, which is a regulator of the cell cycle, as a homolog of yeast securin and a transcriptional activator of several angiogenic factors. Here we examined the relationships of hPTTG1 expression with cell proliferation, expression of the angiogenic factor, VEGF (vascular endothelial growth factor), and numbers of the blood vessels in the normal and/or adenomatous pituitary. With the exception of TSHoma, the expression of hPTTG1 was significantly higher in pituitary adenomas than in the normal pituitary gland. The cell proliferation activity was higher in pituitary adenomas than in the normal pituitary. Pituitary cell proliferation was significantly correlated with the level of hPTTG1 expression in the normal pituitary tissue, but there was no such correlation in the adenomas. The significant correlation of hPTTG1 with the VEGF expression and the numbers of the blood vessels was elucidated in pituitary adenomas. It is particularly noteworthy that immunohistochemical double staining indicated co-localization of VEGF in many hPTTG1-positive tumor cells. In conclusion, higher levels of hPTTG1 expression contribute to the pathobiology of pituitary adenomas by promoting angiogenesis rather than by activating cell proliferation, whereas hPTTG1 expression is related to mitotic activity in the normal pituitary gland.

Securin is not required for chromosomal stability in human cells

Abnormalities of chromosome number are frequently observed in cancers. The mechanisms regulating chromosome segregation in human cells are therefore of great interest. Recently it has been reported that human cells without an hSecurin gene lose chromosomes at a high frequency. Here we show that, after hSecurin knockout through homologous recombination, chromosome losses are only a short, transient effect. After a few passages hSecurin(-/-) cells became chromosomally stable and executed mitoses normally. This was unexpected, as the securin loss resulted in a persisting reduction of the sister-separating protease separase and inefficient cleavage of the cohesin subunit Scc1. Our data demonstrate that securin is dispensable for chromosomal stability in human cells. We propose that human cells possess efficient mechanisms to compensate for the loss of genes involved in chromosome segregation.

Human full-length Securin is a natively unfolded protein

Human Securin, also called PTTG1 (pituitary tumor transforming gene 1 product), is an estrogen-regulated proto-oncogene with multifunctional properties. We characterized human full-length Securin using a variety of biophysical techniques, such as nuclear magnetic resonance, circular dichroism, and size-exclusion chromatography. Under physiological conditions, Securin is devoid of tertiary and secondary structure except for a small amount of poly-(L-proline) type II helix and its hydrodynamic characteristics suggest it behaves as an extended polypeptide. These results suggest that Securin is unstructured in solution and so belongs to the family of natively unfolded proteins. In addition, to gain structural and quantitative insight, we investigated the binding of Securin to p53. Analytical ultracentrifugation and fluorescence anisotropy studies revealed no evidence of any direct interaction between unmodified recombinant Securin and p53 in vitro.

Pituitary tumor transforming gene binding factor: a novel transforming gene in thyroid tumorigenesis

CONTEXT

There are currently no clear markers for the detection of differentiated thyroid cancer and its recurrence. Pituitary tumor transforming gene (PTTG) is a protooncogene implicated in the pathogenesis of multiple tumor types, which stimulates fibroblast growth factor-2 secretion via PTTG binding factor (PBF).

OBJECTIVE

The aim of this study was to ascertain whether PBF expression is associated with thyroid cancer outcome.

DESIGN

PBF expression was measured at the mRNA and protein level. Tissue was collected during surgery, with normal samples being taken from the contralateral lobe. In vitro studies ascertained the ability of PBF to transform cells and form tumors in nude mice and its subcellular localization.

SETTING

The study was conducted at a primary care/referral center.

PATIENTS

Thyroid tumors were collected from a series of 27 patients undergoing surgical excision of papillary and follicular thyroid tumors.

INTERVENTION

No intervention was conducted.

MAIN OUTCOME MEASURE

The expression of PBF in thyroid cancers compared with normal thyroid, hypothesized before the investigation to be raised in tumors, was the main outcome measure.

RESULTS

PBF mRNA expression was higher in differentiated thyroid carcinomas than in normal thyroid (P < 0.001; n = 27) and was independently associated with tumor recurrence (P = 0.002; R(2) = 0.49). PTTG was able to up-regulate PBF mRNA expression in vitro (P < 0.001; n = 12), and stable overexpression of PBF in NIH3T3 cells resulted in significant colony formation (P < 0.001; n = 12). In vivo, stable sc overexpression of PBF induced tumor formation in athymic nude mice.

CONCLUSIONS

PBF is an additional prognostic indicator in differentiated thyroid cancer that is transforming in vitro and tumorigenic in vivo.

A novel molecular marker of pituitary tumor transforming gene involves in a rat liver regeneration

BACKGROUND

Pituitary tumor transforming gene (PTTG), homologous to a mammalian securin, plays a pivotal role in cell transformation, however, its biological function(s) in normal tissues is not fully understood. Because the liver is a regenerative organ, the relevant biological function of PTTG in the liver would be more feasible to understand PTTG. Also, PTTG may be involved in the liver regeneration.

MATERIALS AND METHODS

Expressions of rat hepatic PTTG messengerRNA (mRNA) and cellular immunoreactivities during the cell proliferative period of the liver regeneration both in vitro and in vivo were tested.

RESULTS

PTTG expression of the rat primary hepatocyte was stimulated by HGF in a dose dependent manner, and was suppressed when hepatocyte proliferation was inhibited by transforming growth factor-beta1. A positive PTTG immunoreactive co-localizing with 5-bromo-2'-deoxyuridine (BrdU) in the hepatocyte nucleus was found and there was a concurrent sister chromatin itself by the immunofluorescent labeling of PTTG with cytokeratin 18 (CK18).

DISCUSSION

Since the correlation of PTTG mRNA expression, cell proliferation and immunoreactivity were observed in primary rat cultured hepatocytes, PTTG may be a novel marker of cell proliferation both in vitro and in vivo liver regeneration.